Optical Temperature Sensing With Infrared Excited Upconversion Nanoparticles.

Kory Green,Shuang Fang Lim,Kai Huang,Hai Pan,Gang Han

doi:10.3389/fchem.2018.00416

Abstract

Upconversion Nanoparticles (UCNPs) enable direct measurement of the local temperature with high temporal and thermal resolution and sensitivity. Current studies focusing on small animals and cellular systems, based on continuous wave (CW) infrared excitation sources, typically lead to localized thermal heating. However, the effects of upconversion bioimaging at the molecular scale, where higher infrared intensities under a tightly focused excitation beam, coupled with pulsed excitation to provide higher peak powers, is not well understood. We report on the feasibility of 800 and 980 nm excited UCNPs in thermal sensing under pulsed excitation. The UCNPs report temperature ratiometrically with sensitivities in the 1 × 10−4 K−1 range under both excitation wavelengths. Our optical measurements show a ln(I525/I545) vs. 1/T dependence for both 800 nm and 980 nm excitations. Despite widespread evidence promoting the benefits of 800 nm over 980 nm CW excitation in avoiding thermal heating in biological imaging, in contrary, we find that given the pulsed laser intensities appropriate for single particle imaging, at both 800 and 980 nm, that there is no significant local heating in air and in water. Finally, in order to confirm the applicability of infrared imaging at excitation intensities compatible with single nanoparticle tracking, DNA tightropes were exposed to pulsed infrared excitations at 800 and 980 nm. Our results show no appreciable change in the viability of DNA over time when exposed to either wavelengths. Our studies provide evidence for the feasibility of exploring protein-DNA interactions at the single molecule scale, using UCNPs as a reporter.

Highlights

Many biological processes occurring within intracellular structures may result in changes in the pH, temperature and electrical potential, to name a few
upconversion nanoparticles (UCNPs) absorb at 800 and 980 nm in the near infrared (NIR), exhibit no bleaching, are non-toxic, and are not affected by blinking (Chen et al, 2006; Schubert et al, 2006). Due to this lack of bleaching, UCNPs are well suited for long term monitoring of biological events at the high laser intensity levels employed in single cell imaging, as opposed to a dye that may bleach over time
UCNPs have been used to measure the temperature of the interior nanoenvironment of magnetically heated iron oxide nanoparticles (Dong and Zink, 2014) and have been shown to enable direct measurement of the local temperature with high temporal and thermal resolution (0.3–2.0 K) (Debasu et al, 2013) and (10−5 K−1) sensitivity (Xu et al, 2012) with simple equipment requirements

Summary

INTRODUCTION

Many biological processes occurring within intracellular structures may result in changes in the pH, temperature and electrical potential, to name a few. Find that given the pulsed laser intensities appropriate for single particle imaging, at both 800 and 980 nm, that there are no significant differences in the local heating effects This result is in contrast with that obtained when comparing excitation at both wavelengths under CW excitation. The mixture was heated to 300◦C at a rate of 15◦C/min under dry argon flow, and maintained at 300◦C for 30 min to form the α-NaYF4:40%Yb, 2%Er intermediate UCNPs. After the mixture cooled to room temperature, the α-NaYF4:40%Yb, 2%Er intermediate UCNPs were collected by centrifugal washing with excessive ethanol (7,500 g, 30 min). A control DNA tightrope experiment without near infrared exposure was performed alongside the near infrared exposed DNA tightropes

AND DISCUSSION

Findings

CONCLUSION